Distances between replicate tissues. Histogram of the Euclidean distance between the gene expression values for paired tissue samples. We expect these distances to be fairly small because we assume that, for the most part, the same genes are expressed in samples from the same tissue. In fact, this does appear to be the case - the typical distance between replicate samples is 30. However, one pair of replicate tissues (Cardiac Myocytes) has a distance larger than 90, suggesting one of the samples may be of poor quality.